This invention relates to carpet backings. More particularly, it relates to aqueous dispersed polymeric compositions containing a hydrophobically-modified ethylene-oxide-based urethane block copolymer as a thickener and a method for preparing a carpet backing therefrom.
Carpet processing depends on the rheological properties of the carpet""s various layers. Thickeners are added to affect those Theological properties. Unfortunately, the industry standard thickener is a sodium polyacrylate that adversely affects finished carpet tuftbind and water barrier properties. Accordingly, there is a need for a thickener that imparts excellent carpet processing properties without adversely affecting finished carpet tuftbind and water barrier properties. This need particularly applies to tufted carpets.
Generally, tufted carpets minimally consist of tufted fibers through a primary backing and a precoat. Tufted carpets may also have additional layers such as a laminate layer, a secondary layer, and a foam layer. Moreover, the tufted carpet may have more than one secondary layer.
The precoat is required to anchor the carpet tufts to the primary backing. It may also contain an adhesive to adhere the tufted carpet to additional layers or the subfloor. The precoat can affect the carpet""s tuft bind, hand, delaminating properties, wet strength properties, wear resistance, and barrier performance. Alternatively, a laminate layer may be applied without a precoat. However, better anchoring is achieved when a precoat is also applied than when a laminate layer is applied alone.
Precoat, laminate, and foam layers may be prepared from a butadiene-acrylonitrile latex, an ethylene-vinyl acetate latex, a styrene-butadiene-butyl acrylate latex, a polychloroprene latex, a polyethylene copolymer latex, an ethylene-styrene latex, a styrene-butadiene-vinylidene chloride latex, a styrene-alkyl acrylate latex, a vinyl latex, or an acrylic latex. However, they are usually prepared from a polyurethane material or a styrene-butadiene latex.
With regard to polyurethane layers, conventional practice in the carpet manufacturing industry requires that a polyurethane layer be prepared from an isocyanate formulation (A-side formulation) and a polyol formulation (B-side formulation) at the carpet manufacturing site. This is sometimes referred to as xe2x80x9cA+B chemistryxe2x80x9d. Preparing a polyurethane layer by A+B chemistry requires a substantial investment in specialized equipment to achieve the exceptional performance characteristics of this method.
Alternatively, the polyurethane layer may be applied as an aqueous polyurethane (PU) dispersion. Aqueous PU dispersions can be prepared by polymerizing the polyurethane reactants in an organic solvent followed by dispersion of the resulting solution in water, and optionally followed by removal of organic solvent. See U.S. Pat. Nos. 3,437,624; 4,092,286; 4,237,264; 4,742,095; 4,857,565; 4,879,322; 5,037,864; and 5,221,710, which are incorporated herein by reference. Also, an aqueous polyurethane dispersion may be prepared by first forming a prepolymer, next dispersing the prepolymer in water, and finally conducting a chain extension in the water as disclosed in WO 98/41552, published Sep. 24, 1998, which is incorporated herein by reference. In this instance, the aqueous polyurethane dispersion will preferably have water as a continuous phase. U.S. Pat. No. 4,296,159 to Jenkines, et al., discloses preparing a tufted or woven article having a unitary backing prepared by applying a polyurethane forming composition to the underside of the tufted or woven article.
As a polyurethane dispersion, the polyurethane layer may be applied as a blown formulation. The blown formulation is generally prepared by mixing the A-side components with the B-side components in the presence of a gas, which is either mechanically introduced or chemically produced, to form bubbles that yield a cell-like structure in the cured polyurethane. Mechanical whipping of gas into a polyurethane formulation is also termed xe2x80x9cfrothing.xe2x80x9d
The industry standard sodium polyacrylate thickener improves the rheological properties of carpets prepared with aqueous dispersed polymeric compositions. Unfortunately, it also adversely affects the carpet""s tuftbind and water barrier properties. Accordingly, it is desirable to use a thickener that imparts similar Theological properties without adversely affecting the finished carpet""s tuftbind and water barrier properties.
According to the present invention, an aqueous dispersed polymeric composition for preparing a carpet backing is provided. In the preferred embodiment, the aqueous dispersed polymeric composition comprises an aqueous dispersed polymeric material and a hydrophobically-modified ethylene-oxide-based urethane block copolymer. In the more preferred embodiment, the aqueous dispersed polymeric material is an aqueous polyurethane dispersion composition. Moreover, a method for preparing a carpet backing using the aqueous dispersed polymeric composition is provided.
In the preferred embodiment, the aqueous dispersed polymeric composition for preparing a carpet backing comprises an aqueous dispersed polymeric material and a hydrophobically-modified ethylene-oxide-based urethane block copolymer as a thickener. The aqueous dispersed polymeric material is selected from the group consisting of an aqueous polyurethane dispersion composition, a styrene-butadiene latex, a butadiene-acrylonitrile latex, an ethylene-vinyl acetate latex, a styrene-butadiene-butyl acrylate latex, a polychloroprene latex, a polyethylene copolymer latex, an ethylene-styrene latex, a styrene-butadiene-vinylidene chloride latex, a styrene-alkyl acrylate latex, a vinyl latex, an acrylic latex, and mixtures thereof. In the more preferred embodiment, the aqueous dispersed polymeric material is an aqueous polyurethane dispersion composition.
In the present invention, polyurethane can refer to a polyurethane compound, a polyurea compound, or mixtures thereof. A polyurethane compound can be obtained by the reaction of a polyol with a polyisocyanate. A polyurea compound can be obtained by the reaction of an amine with a polyisocyanate. A polyurethane compound or polyurea compound can contain both urea and urethane functionality, depending on what compounds are included in the A and/or B-side formulations. For the purposes of the present application, no further distinction will be made herein between the polyurethane compounds and polyurea compounds. The term xe2x80x9cpolyurethanexe2x80x9d will be used generically to describe a polyurethane compound, a polyurea compound, and mixtures thereof.
An aqueous polyurethane dispersion composition useful in the practice of the present invention includes water, and a polymeric compound selected from the group consisting of a polyurethane compound, a mixture of polyurethane-forming compounds, and mixtures thereof. Preferably, the aqueous polyurethane dispersion composition will have water as a continuous phase. Polyurethane-forming compounds as used in the present invention are compounds that are capable of forming polyurethane polymers. Polyurethane-forming compounds include, for example, polyurethane prepolymers. Prepolymers useful in the practice of the present invention are prepared by the reaction of active hydrogen compounds with any amount of isocyanate in excess material relative to active hydrogen material. The isocyanate functionality can be present in an amount of from about 0.2 wt % to about 40 wt %. A suitable prepolymer can have a molecular weight in the range of from about 100 to about 10,000. Prepolymers useful in the practice of the present invention should be substantially liquid under the conditions of dispersion.
Active hydrogen compounds can be described as compounds having functional groups that contain at least one hydrogen atom bonded directly to an electronegative atom such as nitrogen, oxygen or sulfur. Suitable active hydrogen compounds can be polyols of molecular weight of less than about 6000.
The aqueous polyurethane dispersion composition as described herein can include chain extenders, catalysts, fillers, filler wetting agents, surfactants, blowing agents, frothing agents, dispersants, foam stabilizers, other thickeners, fire retardants, defoamers, pigments, antistatic agents, reinforcing fibers, antioxidants, preservatives, acid scavengers, and other materials useful in polyurethane formulations. A chain extender is used herein to build the molecular weight of the polyurethane prepolymer by reaction of the chain extender with the isocyanate functionality in the polyurethane prepolymer, i.e., chain extend the polyurethane prepolymer.
A suitable chain extender is typically a low equivalent weight active hydrogen containing compound, having about 2 or more active hydrogen groups per molecule. The active hydrogen groups can be hydroxyl, mercaptyl, or amino groups. An amine chain extender can be blocked, encapsulated, or otherwise rendered less reactive. Other materials, particularly water, can function to extend chain length and so are chain extenders for purposes of the present invention. Polyamines are preferred chain extenders. It is particularly preferred that the chain extender be selected from the group consisting of amine terminated polyethers such as, for example, TEXRIM TR401(trademark) from Huntsman Chemical Company, amino ethyl piperazine, 2-methyl piperazine, 1,5-diamino-3-methyl-pentane, isophorone diamine, ethylene diamine, diethylene triamine, triethylene tetramine, tetraethylene pentamine, ethanolamine, lysine in any of its stereoisomeric forms and salts thereof, hexane diamine, hydrazine and piperazine. In the practice of the present invention, the chain extender is often used as a solution of chain extender in water.
Small amounts of chain extender can be advantageously used. Generally, the chain extender is employed at a level sufficient to react with from about zero (0) to about 100 percent of the isocyanate functionality present in the prepolymer, based on one equivalent of isocyanate reacting with one equivalent of chain extender. It can be desirable, under certain conditions, to allow water to act as a chain extender and react with some or all of the isocyanate functionality present.
A catalyst can be used to promote the reaction between a chain extender and an isocyanate. Suitable catalysts include tertiary amines, organometallic compounds, similar compounds, and mixtures thereof. For example, suitable catalysts include di-n-butyl tin bis(mercaptoacetic acid isooctyl ester), dimethyltin dilaurate, dibutyltin dilaurate, dibutyltin sulfide, stannous octoate, lead octoate, ferric acetylacetonate, bismuth carboxylates, triethylenediamine, N-methyl morpholine, similar compounds, and mixtures thereof. An amount of catalyst is advantageously employed such that a relatively rapid cure to a tack-free state can be obtained. If an organometallic catalyst is employed, such a cure can be obtained by using from about 0.01 to about 0.5 parts per 100 parts of the polyurethane-forming composition, by weight. If a tertiary amine catalyst is employed, the catalyst preferably provides a suitable cure using from about 0.01 to about 3 parts of tertiary amine catalyst per 100 parts of the polyurethane-forming composition, by weight. Both an amine type catalyst and an organometallic catalyst can be employed in combination.
The aqueous polyurethane dispersion composition of the present invention can include conventional fillers such as milled glass, calcium carbonate, aluminum trihydrate, talc, bentonite, antimony trioxide, kaolin, fly ash, or other known fillers. A suitable filler loading in a polyurethane dispersion can be from about 100 to about 1000 parts of filler per 100 parts of the polyurethane compound. Preferably, the filler material can be loaded in an amount of at least about 200 pph, more preferably at least about 300 pph, most preferably at least about 400 pph.
The aqueous polyurethane dispersion composition of the present invention can include a filler wetting agent. A filler wetting agent generally renders the filler material compatible with a polyurethane-forming composition. Useful wetting agents include phosphate salts such as sodium hexametaphosphate. A filler wetting agent can be included in a polyurethane-forming composition of the present invention at a concentration of at least about 0.1 parts per 100 parts of filler, by weight.
Useful surfactants to make aqueous polyurethane dispersion composition include cationic and anionic surfactants. Examples of anionic surfactants include sulfonates, carboxylates, and phosphates. Examples of cationic surfactants include quaternary amines. Surfactants can be either external or internal. External surfactants are not chemically reacted into the polymer during dispersion preparation. Internal surfactants are chemically reacted into the polymer during dispersion preparation. A surfactant can be included in an amount ranging from about 0.01 to about 20 parts per 100 parts by weight of polyurethane component.
Examples of suitable blowing agents are gases such as air, carbon dioxide, nitrogen, argon, and helium; liquids such as water, low molecular weight hydrocarbons, and volatile halogenated alkanes; and azo-blowing agents such as azobis(formamide). Volatile halogenated alkanes include the various chlorofluoromethanes and chlorofluoroethanes. Preferable is the use of air as a blowing or frothing agent. A frothing agent can differ from a blowing agent in that frothing agents are typically introduced by mechanical whipping into the polyurethane formulation.
An aqueous polyurethane dispersion composition of the present invention can be stored for later application to the back of a carpet. Storage for this purpose requires that the dispersion be storage-stable. Alternatively, the polyurethane dispersion can be applied in a continuous manner to the back of a carpet primary backing. That is, the dispersion can be applied to the back of a carpet as the dispersion is obtained. Polyurethane dispersions applied to a carpet in a continuous manner are not required to be storage-stable, and can have higher solids content and/or larger mean particle size than typical storage-stable polyurethane dispersion formulations.
A suitable storage-stable aqueous polyurethane dispersion composition as defined herein is any polyurethane dispersion composition having a mean particle size of less than about 5 micrometers; a more preferable mean particle size is less than about 1 micrometer. A polyurethane dispersion that is not storage-stable can have a mean particle size of greater than 5 micrometers. For example, a suitable dispersion can be prepared by mixing a polyurethane prepolymer with water and dispersing the prepolymer in the water using a commercial blender. Alternatively, a suitable dispersion can be prepared by feeding a prepolymer into a static mixing device along with water, and dispersing the water and prepolymer in the static mixer. Continuous methods for preparing aqueous dispersions of polyurethane are known and can be used in the practice of the present invention. For example, U.S. Pat. Nos. 3,437,624; 4,092,286; 4,237,264; 4,742,095; 4,857,565; 4,879,322; 5,037,864; and 5,221,710 describe continuous processes useful for obtaining aqueous polyurethane dispersions. In addition, a continuous process for preparing an aqueous polyurethane dispersion having a high internal phase ratio is described in U.S. Pat. No. 5,539,021, incorporated herein by reference.
In preparing a frothed polyurethane backing, it is often preferable to premix all of the components except the polyisocyanate (and the blowing agent when a gas is used) to form a xe2x80x9cBxe2x80x9d component. The polyisocyanate and the B component are admixed and then the blowing agent gas is blended in using, for example, an OAKES FROTHER* (*OAKES FROTHER is a trade designation of the E.T. Oakes Corporation). The composition is preferably applied to a textile or other substrate prior to any significant level of curing using equipment such as a doctor knife, air knife, or extruder to apply and gauge the layer. In the alternative, the composition may be applied by (1) forming it into a layer on a moving belt or other suitable apparatus, (2) dehydrating or partially curing, and (3) finally, marrying it to the carpet primary backing. It may be married to the carpet primary backing with equipment such as a double belt laminator (also known as double band) or a moving belt with an applied foam cushion. The polyurethane is then allowed to cure by applying heat by means of an infrared oven, open flame forced draft convection impingement oven, heated plates or the like.
In preparing polyurethane-backed carpets according to the present invention, an aqueous polyurethane dispersion is applied as a layer of preferably uniform thickness onto one surface of a carpet primary backing. Aqueous polyurethane dispersions of the present invention can be applied as a precoat, a laminate layer, or a foam layer. Polyurethane precoats, laminate layers, and foam layers can be prepared by methods known in the art. Precoats, laminate layers and foam layers prepared from latexes are described in P. L. Fitzgerald, xe2x80x9cIntegral Latex Foam Carpet Cushioningxe2x80x9d, J. Coat. Fab. 1977, Vol. 7 (pp.107-120), and in R. P. Brentin, xe2x80x9cLatex Coating Systems for Carpet Backingxe2x80x9d, J. Coat. Fab. 1982, Vol. 12 (pp. 82-91).
The polyurethane-forming composition can be applied to one surface of a carpet primary backing before it cures to a tack-free state. Alternatively, a polyurethane dispersion containing no unreacted isocyanate functionality can be applied, thereby removing the need to cure the polymer. Typically the polyurethane-forming composition is applied to the surface attached to a primary backing. The amount of polyurethane-forming composition used can vary widely, from about 5 to about 500 ounces per square yard (0.17 to 16.95 kg/sq. meter), depending on the characteristics of the textile.
A styrene-butadiene latex useful for practicing the present invention is disclosed in P. L. Fitzgerald, xe2x80x9cIntegral Latex Foam Carpet Cushioningxe2x80x9d, J. Coat. Fab. 1977, Vol. 7 (pp.107-120) and in R. P. Brentin, xe2x80x9cLatex Coating Systems for Carpet Backingxe2x80x9d, J. Coat. Fab. 1982, Vol. 12 (pp. 82-91), both incorporated herein by reference. A styrene-butadiene-vinylidene chloride latex useful for practicing the present invention is disclosed in U.S. Pat. No. 5,741,393, incorporated herein by reference.
U.S. Pat. No. 5,770,660, incorporated herein by reference, discloses a method for preparing a butadiene-acrylonitrile latex that is useful for practicing the present invention. U.S. Pat. Nos. 3,644,262 and 4,164,489, incorporated herein by reference, disclose methods for preparing ethylene-vinyl-acetate latexes that are useful for practicing the present invention. U.S. Pat. No. 5,591,806, incorporated herein by reference, discloses a method for preparing an ethylene acrylic acid aqueous dispersion that is useful for practicing the present invention.
U.S. Pat. Nos. 3,890,261 and 5,661,205, incorporated herein by reference, disclose methods for preparing polychloroprene latexes useful for practicing the present invention. U.S. Pat. No. 5,380,785, incorporated herein by reference, discloses a method for preparing a butyl acrylate-acrylonitrile-styrene latex that is useful for practicing the present invention. U.S. Pat. Nos. 4,689,256 and 5,300,551, incorporated herein by reference, disclose methods for preparing vinyl chloride polymer latexes that are useful in practicing the present invention.
U.S. Pat. No. 5,591,806, incorporated herein by reference, discloses a method for preparing a ethylene acrylic acid copolymer latex that is useful in practicing the present invention. U.S. Pat. No. 4,714,728, incorporated herein by reference, discloses a method for preparing an aqueous dispersion of acidic ethylene interpolymers that are useful in practicing the present invention.
U.S. Pat. No. 4,228,058, incorporated herein by reference, discloses a method for preparing a mixture of vinylidene chloride latex and a styrene-butadiene latex useful in practicing the present invention. Other methods of preparing useful aqueous dispersed polymeric compositions would be readily apparent to a person of ordinary skill in the art in view of this disclosure. Those methods and aqueous dispersed polymeric compositions are within the scope of the invention with regard to preparing useful aqueous dispersed polymeric compositions.
The hydrophobically-modified ethylene-oxide-based urethane block copolymer of the present invention is a thickener that imparts excellent rheological properties to the aqueous polyurethane dispersion without adversely affecting the finished carpet""s tuftbind and water barrier properties. Examples of the thickeners are available commercially from Rohm and Haas Company under the ACRYSOL(trademark) trademark. Specific examples of ACRYSOL(trademark) thickeners are shown in TABLE 1.
The thickener can be added to the carpet backing formulation mixture in an amount of from 0.01 parts to about 1.5 parts, based on parts of thickener solids per hundred parts of polymer solids. Preferably the thickener is added in an amount of from about 0.05 parts to about 1.0 parts, more preferably form about 0.1 parts to about 0.75, and most preferably from about 0.2 parts to about 0.5 parts.
The thickeners can be added alone or mixed with other thickeners to give the desired Newtonian or non-Newtonian rheological response. For Newtonian flow characteristics, RM 825, RM 8W, RM 1020, and RM 2020 NPR are preferred. These thickeners are used alone or, preferably, diluted with water to about 10 to about 15% solids to prevent compound shocking as the thickener is added. For non-Newtonian flow characteristics, SCT 275 or RM 12W is preferred. These thickeners are also diluted with water to reduce compound. The most preferred thickener is a blend of RM 8W with RM 12W in a 1:2 ratio. The blended thickener is diluted with water to a mixture having about 13.2% solids. Notably, the blended thickener provides a modified non-Newtonian response at very low levels of thickener solids (about 0.5 part per hundred polymer).
The embodiments described herein are given to illustrate the scope and spirit of the present invention. The embodiments herein will make apparent to those skilled in the art other embodiments that may also be used. These other embodiments are within the scope of the present invention. Thus, the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the embodiments given herein.